1. Field of the Invention
This invention relates to a system of medical devices intended for being at least partly implanted into a living body and comprising at least two modules which are interconnected by a communication transmission channel denoted the "body bus".
2. Description of the Prior Art
Devices of this type are known in different embodiments, e.g. EPO 0 011 935 and EPO 0 011 936 describe an external programming device and an implantable electromedical device adapted for being programmed thereby, wherein the programming device comprises a transmitting antenna, and the implantable device comprises a receiving antenna which are mutualy aligned with each other for programming in order to transcutaneously transmit high frequency programming signals in the form of electromagnetic waves from the transmitting antenna to the receiving antenna. In view of the fact that high frequency electromagnetic waves are heavily attenuated or screened by body tissue, the implanted receiving antenna must be exactly located for programming. Such a procedure is particularly troublesome if a plurality of programmable modules, e.g. a pacemaker, a defibrillator and a drug dispensing device, are implanted, the receiving antennas of which must be individually located.
In the case of a prior muscle stimulation apparatus (U.S. Pat. No. 4,524,774) in a similar manner, muscle potentials detected by implanted sensors are converted by a modulator into control signals for a telemetry transmitter which is integrated into the respective sensor. This telemetry transmitter transcutaneously transmits high frequency telemetry signals to an external telemetry receiver which is connected to a data processing unit. The latter, on the base of the received signals, controls a likewise externally disposed telemetry transmitter for delivering high frequency control signals, against transcutaneously, to receivers of implanted muscle stimulators. The transcutaneously transmitted signals are in the megacycles/sec. frequency range so that the aforementioned restrictions are encountered in this case too.
Furthermore, it is known (FIG. 1 of U.S. Pat. No. 4,543,955) to transmit measuring signals of an implanted sensor module through a wire connection to another implanted module, such as a pacemaker or a drug delivery device. This requires, during implantation, a troublesome wiring of connection conduits. Furthermore if an infection occurs at one of the implanted modules, all modules and connection conduits must be removed because the infection can spread along the connection conduits. In conformity with modified embodiments of the last mentioned device (FIGS. 2 and 5 of U.S. Patent 4,543,955) measuring signals, which have been converted into a program code, also can be unidirectionally transmitted, in a wireless manner, from the sensor to the pacemaker or to the drug dispensing device, wherein either the signals defining the program code are directly transmitted through body tissue (i.e., without any carrier) or again a high frequency transmitter is used. A carrier free signal direct transmission, for being effective, must be carried through during the refractory phases, i.e. must be synchronized with the heart cycle because otherwise the signals required for such a direct transmission may provoke undesired biological reactions. On the other hand, the high frequency transmission, in this case too, poses problems because of the heavy attenuation caused by body tissue and is possible, if at all, merely if the transmitting and receiving antennas are closely spaced with in the body.
In addition, it is known from U.S. Pat. No. 4,787,389 to provide implantable defibrillator-pacemaker system where the defibrillator's operation is controlled by the separately implanted pacemaker. Signal transmission is effected by coded pulse trains as in U.S. Pat. No. 4,593,955.